Synthesis, characterization, rheological and self-assembly behavior of polyelectrolytes hydrophobically modified with high styrene content: Effect of external parameters on thickening properties and nano-associations

Abstract

Acrylamide (AM)/2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS)/styrene (St) (AMAS) and AM/sodium styrenesulfonate (SSS)/St (AMSS) polyelectrolytes were synthesized by micellar copolymerization method and then characterized using 1H-NMR, rheometry, viscometry, dynamic light scattering (DLS) and water solubility analyses. It was found that polyelectrolytes are not soluble in the water due to their high length of St blocks (NH=15.4); however, a significant self-assembly behavior of St nano-sized associations was observed by adding a low amount of SDS (10 mM) to the aqueous solution, resulting in the improved rheological behavior of the corresponding solutions. Effect of the external stimuli including emulsifier (SDS) and electrolyte (NaCl) concentration and temperature on the reduced viscosity of polyelectrolyte solutions was also studied using I-optimal design. Based on the viscosity measurements, notable thickening ability for aqueous solutions of both the AMAS and AMSS samples were observed at a SDS concentration of 6.5 mM, NaCl concentration of 0.55 wt% and temperature of 25 °C, which was further confirmed using oscillatory frequency sweep and dynamic light scattering measurements. Moreover, the higher thickening ability was observed for the AMSS aqueous solution in comparison with the AMAS one.